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Hi all, I'm new to this forum, and new to 4 wheelers. I recently bought a 04 Foreman 450. It would start real easy, but smoked like crazy. So I put a new piston and rings in, had the cylinder bored etc... Anyway, ever since I got it all back together, I can start it when it's cold ath the beginning of the day, and it will run fine for a few minutes, with no smoke or odd noises, then it will die, and I am not able to restart it untill the next day, after it sitting over night. I'm out of ideas

I've double checked that the fuel is on, and it flows well to the carb. the carb has been gone through and thoroughly cleaned, it's got a new spark plug, I've double checked the valves, and they are both at .006" I've tried a different coil, a different carb, different CDI (used)

I have no idea what else to do/check and hope you guys can point me in the right direction. Thanks for your help
 

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welcome to the forum
1st thing i would do is check the compression both hot and cold (see if it differs)
2ndi would makesure there is no restrision in the muffler
3rd id change the sparkplug (if cracked it can stop working when it gets hot it expans)
 

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Compression is at 148 cold, I will try to check it hot tommorrow.
I will check the muffler, however, it originally had a straight pipe on it (there when I bought it) and it did the same thing with it on there. It's got a used factory muffler on it now.
I have tried two different spark plugs, one came with the bike, the other brand new, no noticalbe cracks or deffects in either one, it has not run enought to color/discolor the new plug yet. Spark plug gap is set to .035 Also I've noticed that the plug is dry when I pull it out after it dies, I expected it to be wet, from attempting to start it, I thought it might have gotten flooded after cranking it for a little bit, but it was totally dry.
 

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if i push the primer on the carb ( I can hear it squirt) it will sputter also. But without doing that or spraying starter fluid, nothing.
 

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The carb was dissassembled and soaked in carb acid, and then thoroughly cleaned with aerosol carb cleaner, and then reassembled. I even tried a second carb, it was not soaked but was cleaned with aerosol carb cleaner.
 

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Welcome to the forum. Great machine choice. Hopefully it's just a carb issue like Rich is thinking. Often times many posters have had to flush multiple times to get it going.
 

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Could it be vapour locking?? Next time it dies open the fuel tank and listen for air rushing in the tank.
 

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wile running spray carb clean on boot , if idle picks up you gota leak
good luck......RICH
The boot checked out fine, no cracks, and spraying it did not effect the idle at all.


It runs great when it's cold each morning, but warms up and nothing. I don't know how the whole ignition system works, but is there some sort of sensor for the crank or cam position? or an engine temp sensor? If so could one of those be bad, and cause it that when it warms up that the electronic timing is off a little bit? What's the best way to check the physical timing? I don't think it's off though, as it runs great, and has tons of power, when it's actually running.

It's not vapor locking, as soon as it dies, I can open the bowl drain, and fuel comes out, and the carb doesn't get very hot, certainly not hot enough to vapor lock internally in the carb, and the fuel line doesn't get warm at all.
Thanks for all your replies and suggestions thus far....
 

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After it dies and won't start back, have you checked to see if it's firing at the spark plug? That will tell you if it's an ignition problem.

I don't know how the whole ignition system works, but is there some sort of sensor for the crank or cam position? or an engine temp sensor?
There's a pulse generator (pickup coil) that measures the angle of the crank. That's what tells the ignition system when to fire. It's possible that it or the ignition coil could be getting hot and breaking down.

Have you checked the valve clearance since you put it back together? Maybe the valves are too tight and when the engine heats up, they expand and hold the valves open slightly. That might not be the problem, but I would check them anyway to eliminate the problem, if you haven't already.

All that being said, the fact that you said that the spark plug isn't wet after tying to start it, makes me think it's a fuel problem. The next time it quits, check for a spark at the spark plug and they should help you determine if it's an ignition problem or a fuel problem.
 
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